The type of wells that benefit most from fracking are: a) completed production wells in suitable oil and/or gas containing formations; and b) “injection wells,” oil wells that have already undergone secondary or tertiary “recovery operations.” Such operations involve injecting water or gas at a (preferably remote) “injection well” to drive hydrocarbon flow to the collection well. Fracking at the injection well may facilitate the transport of these fluids through the subterranean formations.
Several methods are known to moderate hydraulic fracturing fluid breaking kinetics. These methods rest upon moderating the escape of breaking chemicals from capsules that have been placed in the hydraulic fracturing fluid. No method eliminates all the problems described above.
U.S. Pat. No. 5,373,901 discloses a method of controlling the breaking of an aqueous fracturing fluid with an encapsulated breaker. The breaker described therein is encapsulated within a water-insoluble membrane that contains water-insoluble solid particles. This method teaches that when this membrane is exposed to at least one fluid to which the membrane is soluble, the embedded solid particle “imperfections” begin to exit the membrane, creating pores. The fluid can be indigenous to the subterranean formation, or in an introduced carrier fluid. As the fluid enters the capsule through the pores, the encapsulated breaker dissolves into the fluid's aqueous component, which in turn diffuses outward, beginning the breaking of the fracturing fluid gel. This method, however, leaves unwanted solid membrane-embedded particles in the fracture, which may inhibit the free flow of oil.
U.S. Pat. No. 4,202,795 discloses a pellet comprised of a solid, hydratable gelling agent encasing a chemical breaking agent. The approach taken in U.S. Pat. No. 4,202,795 is degradation of the protective gel encapsulant from within by the encapsulated breaker. Release kinetics are modulated by varying the types, and amounts, of protective hydratable gelling agents enveloping the breaker chemicals. We note that this method tends to release all of the breaking fluid at once, which may cause premature breaking
U.S. Pat. No. 4,506,734 teaches a method for reducing hydraulic fracturing fluid viscosity by placing a viscosity-reducing chemical in hollow, fragile beads that may optionally be porous. When the fracturing fluid pressure is released, the newly-created fractures close to some extent, crushing the fragile beads, releasing the viscosity-reducing chemical. Breaker release depends upon the formation's closure pressure, which in turn depends upon the nature of the subterranean structure and its closure rate. This method uses a gelling agent that is hydrated forming a protective gel around said pellets for the period. When the gel breaks down the breaker is released. Thus, this method is not a controlled release, but a delayed release.
U.S. Pat. No. 4,741,401 discloses a hydraulic fracturing fluid breaking method involving the placement of a capsule comprising an enclosure member containing the breaker into the fluid injected into the subterranean formation. The enclosure member is sufficiently permeable to at least one fluid present either in the subterranean environment, or present in the hydraulic fracturing fluid. Osmotic pressure drives that fluid through the enclosure membrane, and upon sufficient fluid intake the capsule ruptures, disgorging the breaker. As with the method taught in U.S. Pat. No. 4,202,795, this method tends to release substantially all the encapsulated breaker at one time, which is associated with premature breaking.
U.S. Pat. No. 4,770,796 teaches a method for breaking fracturing fluid compositions comprising a polymer cross-linked with titanium or zirconium crosslinking agents. An acidic breaker compound is encapsulated in a composition comprising a cellulosic material and a fatty acid and optionally, a wax. A shortcoming of this method is that insoluble cellulosic residue remains in the fractures, impeding fluid flow and could potentially damage the formation
U.S. Pat. No. 4,919,209 discloses a method limited to the breaking of oil-based fracturing fluid gels, which comprises injecting a breaker capsule comprising an enclosure member enveloping a breaker into the formation. The enclosure member is sufficiently permeable to at least one fluid in the formation or the gelled oil fracturing fluid, such that the enclosure member dissolves, thereby releasing the breaker
U.S. Pat. No. 5,164,099 discloses a method utilizing a polyamide membrane to encapsulate a percarbonate, perchlorate or persulfate breaker. The polyamide membrane is permeable to at least one fluid in the formation which dissolves the breaker. The breaker then diffuses through the membrane to break the fracturing fluid. The polyamide membrane is sufficiently durable that it remains intact during, and after, the breaker release, which may inhibit the free flow of hydrocarbon and injected fluids. Most preferred permeable membranes are acrylamide polymers, whereas, this is a nylon membrane. Emulsions or solutions of nylon are not readily and commercially available.
There is a need for a method for the breaking of fracturing fluids which is economical, provides controlled breaker release, minimizes damage to the hydrocarbon-bearing formation, and finally, does not create any hindrance to the flow hydrocarbon or injection fluids in the subterranean structure.